Duvet covers having down insulation trapped between the base sheet and top sheet of the duvet cover are well known in the art. It is also well known that down feathers provide excellent insulating properties. The higher the fill power (fluffiness) of the down and therefore the more air trapped in the down, the more insulating ability an ounce of the down will have. Down is also a very light product that is desirable for insulation and particularly with products wherein weight is a factor, such as articles of apparel, sleeping bags, duvet covers, etc. However, down is a difficult product to work with due to its fluffy nature and unstable condition. It can also be hazardous to one's health has its fluffy miniscule filaments easily propagate into the surrounding air. For this reason work personnel are advised to wear breathing masks.
Articles of apparel and bedding manufactured with down feather insulation are constructed by entrapping the down between opposed fabric sheets. To prevent the down from displacement, the fabric sheets are sewn with quilt stitched patterns. Some of these patterns are produced by cross-stitches to form small pockets in which the down feathers are trapped. See U.S. Pat. No. 5,692,245 as an example. With bedding products, such as a duvet cover, the quilt stitches may be spaced apart from about 1 inch to 10 inches forming pockets with loose down therein. During use of these products, the down shifts within the pockets and form areas where the down is concentrated and other areas where there is much less down or no down. This results in areas where there is too much insulation or not enough insulation. Furthermore, because the down is loose between the fabric sheets at the time of stitching, the down is not uniformly distributed between the fabric sheets resulting in stitching being done over heavy down underlay or no down at all creating irregularities in the stitched seams which are visible to the eye or resulting in a rejection of the manufactured product. Because duvet covers are made with large cross stitched quilt patterns and consequently large pockets for retaining the down, the down will propagate to corners of these pocket and unevenly therein. In the case of duvet covers having no quilt stitches, the down always propagate into regions and it is then necessary to shake the duvet in an attempt to distribute the down substantially evenly therein but such is near to impossible. Accordingly, the duvet cover has to be shaken constantly due to the unstable nature of the down.
A further problem with duvet covers is that when they are washed, the loose feathers or down absorbs water and the mechanical action of a drying machine is not desirable for the down as the duvet cover is subjected to a tumbling and stretching action. Therefore, it is best to let the duvet cover dry in the open air to maintain a duvet cover with a uniform appearance. Dry cleaning is an option which is more costly and also is not desirable down duvet covers. Accordingly, the useful life of the duvet cover is reduced when subjected to washing and drying
There is also a need to have a duvet cover wherein the thermal insulation factor can be modified throughout the duvet cover or in designated parts thereof to suit individual preferences and/or calibrate the insulation of the duvet cover to the cnhanging seasons.
U.S. Pat. No. 6,025,041 addresses the problem of using the loose fluffy down feathers in the manufacture of articles and relates to a method of forming a down feather sheet of substantially constant thickness and particularly for use in the fabrication of articles of apparel such as described in U.S. Pat. No. 5,692,245.
It is also desirable with duvet covers to provide different thermal properties for each sleeping side of a bed, as is described and demonstrated in US Patent Publication 2005/0268399. It is also well known that the body of a person, when sleeping, requires less covering and thermal insulation in certain sections of its body.
It would also be desirable to manufacture light weight duvet covers having esthetically pleasing stitch patterns and designs without concern to the size of the spaces formed between the design pattern stitch seams where loose down feathers could be unstable or the complexity of the stitch patterns.